Apple has released a public beta of its Safari 4 web browser today, which comes loaded with a new JavaScript engine and support for the latest web standards.

The Cupertino, California-based firm said that the engine, dubbed “Nitro”, runs JavaScript 4.2 times faster than Safari 3.

It also claimed that Nitro executes JavaScript 30 times faster than Internet Explorer 7, and three times faster than Firefox 3.

However, it admitted performance would vary and was dependent on system config, network connection and "other factors”.

Apple unsurprisingly tested Nitro’s abilities on an Intel-based iMac. But more interestingly, the machine was running Microsoft’s rival operating system Vista.

Other new features packed into Safari 4 include Top Sites that give the surfer a visual preview of frequently visited pages, full history search and improved tab browsing.

The browser, which is compatible with Mac OSX and Windows XP SP2 or Vista, supports HTML 5 to allow web-based apps to run offline. It also come with CSS 3 to enable web graphics using reflections, gradients and precision masks.

Apple also took the opportunity today to remind world+dog that the newest browsers, including Google’s Chrome, are based on the firm’s own open source WebKit technology.

Black sweater-wearing beta poets can get their hands on the release here. ®